The good news is that David Tennant is sticking with the role for
another two seasons. The bad news is that there’s going to be
practically a two year hiatus between the fourth and fifth season as
David Tennant tickles his acting bone for the Royal Shakespeare Company.
Here’s the details:

“The schedule for future episodes, according to the BBC, is for the
fourth season to air in the UK in the spring of 2008 along with a
Christmas special, three specials in 2009, and the fifth series in
2010.”

Full story:
http://www.icv2.com/articles/news/11227.html

By E-G 421